Extreme conservation leads to recovery of the Virunga mountain gorillas

As wildlife populations are declining, conservationists are under increasing pressure to measure the effectiveness of different management strategies. Conventional conservation measures such as law enforcement and community development projects are typically designed to minimize negative human influences upon a species and its ecosystem. In contrast, we define "extreme" conservation as efforts targeted to deliberately increase positive human influences, including veterinary care and close monitoring of individual animals. Here we compare the impact of both conservation approaches upon the population growth rate of the critically endangered Virunga mountain gorillas (Gorilla beringei beringei), which increased by 50% since their nadir in 1981, from approximately 250 to nearly 400 gorillas. Using demographic data from 1967-2008, we show an annual decline of 0.7%±0.059% for unhabituated gorillas that received intensive levels of conventional conservation approaches, versus an increase 4.1%±0.088% for habituated gorillas that also received extreme conservation measures. Each group of habituated gorillas is now continuously guarded by a separate team of field staff during daylight hours and receives veterinary treatment for snares, respiratory disease, and other life-threatening conditions. These results suggest that conventional conservation efforts prevented a severe decline of the overall population, but additional extreme measures were needed to achieve positive growth. Demographic stochasticity and socioecological factors had minimal impact on variability in the growth rates. Veterinary interventions could account for up to 40% of the difference in growth rates between habituated versus unhabituated gorillas, with the remaining difference likely arising from greater protection against poachers. Thus, by increasing protection and facilitating veterinary treatment, the daily monitoring of each habituated group contributed to most of the difference in growth rates. Our results argue for wider consideration of extreme measures and offer a startling view of the enormous resources that may be needed to conserve some endangered species.     

Distribution of transferrin C subtypes among the Bedouin and non-Bedouin populations of Jordan

The distribution of transferrin C subtypes was studied in the population of Jordan. The sample comprised 121 Bedouins and 382 other Jordanians from Amman. The frequency of TfC2 was found to be 0.26 among the Bedouins and 0.23 among the non-Bedouin population. TfD was present in low frequency (0.005) among both the Bedouin and non-Bedouin populations.     

Sex preselection: high-speed flow cytometric sorting of X and Y sperm for maximum efficiency

Sex preselection that is based on flow-cytometric measurement of sperm DNA content to enable sorting of X- from Y-chromosome-bearing sperm has proven reproducible at various locations and with many species at greater than 90% purity. Offspring of the predetermined sex in both domestic animals and human beings have been born using this technology since its introduction in 1989. The method involves treating sperm with the fluorescent dye, Hoechst 33342, which binds to the DNA and then sorting them into X- and Y-bearing-sperm populations with a flow cytometer/cell sorter modified specifically for sperm. Sexed sperm are then used with differing semen delivery routes such as intra-uterine, intra-tubal, artificial insemination (deep-uterine and cervical), in vitro fertilization and embryo transfer, and intra-cytoplasmic sperm injection (ICSI). Offspring produced at all locations using the technology have been morphologically normal and reproductively capable in succeeding generations. With the advent of high-speed cell sorting technology and improved efficiency of sorting by a new sperm orienting nozzle, the efficiency of sexed sperm production is significantly enhanced. This paper describes development of the these technological improvements in the Beltsville Sexing Technology that has brought sexed sperm to a new level of application. Under typical conditions the high-speed sperm sorter with the orienting nozzle (HiSON) results in purities of 90% of X- and Y-bearing sperm at 6 million sperm per h for each population. Taken to its highest performance level, the HiSON has produced X-bearing-sperm populations at 85 to 90% purity in the production of up to 11 million X-bearing-sperm per h of sorting. In addition if one accepts a lower purity (75 to 80%) of X, nearly 20 million sperm can be sorted per h. The latter represents a 30 to 60-fold improvement over the 1989 sorting technology using rabbit sperm. It is anticipated that with instrument refinements the production capacity can be improved even further. The application of the current technology has led to much wider potential for practical usage through conventional and deep-uterine artificial insemination of many species, especially cattle. It also opens the possibility of utilizing sexed sperm for artificial insemination in swine once low-sperm-dose methods are perfected. Sexed sperm on demand has become a reality through the development of the HiSON system.     

Genetic conservation of small populations of the endemic tree <Emphasis Type="Italic">Swartzia glazioviana</Emphasis> (Taub.) Glaz. (Leguminosae) in the Atlantic Forest

Swartzia glazioviana is a threatened legume tree species from the Brazilian Atlantic Forest characterized by aggregations of individuals and endemism to an area with extensive human occupation. It is critical to conduct studies on the species to conserve the remaining populations. Using ten nuclear microsatellite loci, we examined the genotypic and genetic diversity and structure, inbreeding, stand-level spatial genetic structure (SGS), effective population size, mating system, and pollen flow in three isolated remnant populations, aiming to inform conservation strategies. All adult individuals found in the populations were mapped and sampled and open-pollinated seeds were collected from two populations. The genotypic diversity (>0.85) indicates that sexual reproduction is predominant and the short distance between ramets indicates that asexual reproduction occurs by root development. In general, populations present SGS which is explained, in part, by root development. The genetic differentiation among populations was greater between more distant populations, suggesting a gene dispersal pattern of isolation by distance. Pollen flow (>27%) indicates that populations are not reproductively isolated, but fertilization followed an isolation by distance pattern. The outcrossing rate was high (\({t_m}\)?>?0.8), but some mating occurred among related individuals (\({t_m}\; - \;{t_s}\)?>?0.1) and were correlated (\({r_p}\)?>?0.15), indicating inbreeding and varying levels of relatedness within families. Inbreeding was higher in seed cohorts than adults, suggesting selection against inbred individuals between seed and adult stages. The results are discussed considering in situ conservation and strategies for seed collection for environmental reforestation.     

Mitochondrial introgression and incomplete lineage sorting through space and time: phylogenetics of crotaphytid lizards

We investigate the roles of mitochondrial introgression and incomplete lineage sorting during the phylogenetic history of crotaphytid lizards. Our Bayesian phylogenetic estimate for Crotaphytidae is based on analysis of mitochondrial DNA sequence data for 408 individuals representing the 12 extant species of Crotaphytus and Gambelia. The mitochondrial phylogeny disagrees in several respects with a previously published morphological tree, as well as with conventional species designations, and we conclude that some of this disagreement stems from hybridization-mediated mitochondrial introgression, as well as from incomplete lineage sorting. Unidirectional introgression of Crotaphytus collaris (western collared lizard) mitochondria into C. reticulatus (reticulate collared lizard) populations in the Rio Grande Valley of Texas has resulted in the replacement of ancestral C. reticulatus mitochondria over approximately two-thirds of the total range of the species, a linear distance of approximately 270 km. Introgression of C. collaris mitochondria into C. bicinctores (Great Basin collared lizard) populations in southwestern Arizona requires a more complex scenario because at least three temporally separated and superimposed introgression events appear to have occurred in this region. We propose an "introgression conveyor" model to explain this unique pattern of mitochondrial variation in this region. We show with ecological niche modeling that the predicted geographical ranges of C. collaris, C. bicinctores, and C. reticulatus during glacial maxima could have provided enhanced opportunities for past hybridization. Our analyses suggest that incomplete lineage sorting and/or introgression has further confounded the phylogenetic placements of additional species including C. nebrius, C. vestigium, C. insularis, C. grismeri, and perhaps G. copei. Despite many independent instances of interspecific hybridization among crotaphytid lizards, the species continue to maintain morphological and geographic cohesiveness throughout their ranges.     

Rapid, automated separation of specific bacteria from lake water and sewage by flow cytometry and cell sorting.

The use of fluorescence-activated flow cytometric cell sorting to obtain highly enriched populations of viable target bacteria was investigated. Preliminary studies employed mixtures of Staphylococcus aureus and Escherichia coli. Cells of S. aureus, when mixed in different proportions with E. coli, could be selectively recovered at a purity in excess of 90%. This was possible even when S. aureus composed only approximately 0.4% of the total cells. Cell sorting was also tested for the ability to recover E. coli from natural lake water populations and sewage. The environmental samples were challenged with fluorescently labelled antibodies specific for E. coli prior to cell sorting. Final sample purities of greater than 70% were routinely achieved, as determined by CFU. Populations of E. coli released into environmental samples were recovered at greater than 90% purity. The use of flow cytometry and cell sorting to detect and recover viable target bacteria present at levels of less than 1% within an indigenous microflora was also demonstrated.     

Prior selfing and the selfing syndrome in animals: an experimental approach in the freshwater snail Biomphalaria pfeifferi.

Inbreeding species of hermaphroditic animals practising copulation have been characterized by few copulations, no waiting time (the time that an isolated individual waits for a partner before initiating reproduction compared with paired individuals) and limited inbreeding (self-fertilization) depression. This syndrome, which has never been fully studied before in any species, is analysed here in the highly selfing freshwater snail Biomphalaria pfeifferi. We conducted an experiment under laboratory conditions over two generations (G1 and G2) using snails sampled from two populations (100 individuals per population). G1 individuals were either isolated or paired once a week (potentially allowing for crosses), and monitored during 29 weeks for growth, fecundity and survival. Very few copulations were observed in paired snails, and there was a positive correlation in copulatory activity (e.g. number of copulations) between the male and female sexual roles. The waiting time was either null or negative, meaning that isolated individuals initiated reproduction before paired ones. G2 offspring did not differ in hatching rate and survival (to 28 days) between treatments, but offspring from paired individuals grew faster than those from isolated individuals. On the whole, the self-fertilization depression was extremely low in both populations. Another important result is that paired G1 individuals began laying (selfed) eggs several weeks prior to initiating copulation: this is the first characterization of prior selfing (selfing initiated prior to any outcrossing) in a hermaphroditic animal. A significant population effect was observed on most traits studied. Our results are discussed with regard to the maintenance of low outcrossing rates in highly inbreeding species.     

Purification of transiently transfected cells by magnetic affinity cell sorting

A method was developed to purify transiently transfected HeLa cells or African green monkey kidney CV-1 cells by magnetic affinity cell sorting. Monolayer cultures were transfected with mammalian expression vectors coding for either of two novel cell surface antigens, the Tac subunit of the human IL-2 receptor or vesicular stomatitis virus G protein. During the transient expression phase, cell populations were placed in suspension and mixed with monoclonal-antibody-coated magnetic particles in the presence of a sorting solution designed to minimize nonspecific cell/cell and cell/particle interactions. Transfected cells expressing the vector-encoded cell surface antigen were then isolated by application of a magnetic field. Reconstruction experiments indicated that IL-2 receptor-positive cells were bound about 100-fold more efficiently than receptor-negative cells. In transient transfection experiments, populations of greater than 90% antigen-positive cells were reproducibly obtained.     

Morphological and genetic predictors of parental care in the North American barn swallow Hirundo rustica erythrogaster

Sexually dimorphic traits often signal the fitness benefits an individual can provide to potential mates. In species with altricial young, these signals may also predict the level of parental care an individual is expected to provide to shared offspring. In this study, we tested three hypotheses that traditionally relate sexually dimorphic traits to parental care in two populations of North American barn swallows Hirundo rustica erythrogaster. The good parent hypothesis predicts a positive relationship between an individual's ornamentation and his or her care whereas the differential allocation (more care given by individuals when paired to high quality mates) and reproductive compensation (more care given by individuals when paired to low quality mates) hypotheses predict that an individual's level of parental investment is relative to the quality of their mate. Male and female North American barn swallows have colorful ventral feathers and elongated tail streamers, but there is evidence that ventral color, not tail streamer length, predicts measures of seasonal reproductive success. Accounting for the positive correlation between within‐pair feeding rates and other potentially confounding variables in all of our models, we found no support for the good parent hypothesis because in both males and females, traits shown to be under sexual selection did not predict feeding rates in either sex. However, our data reveal that male coloration, and not streamer length, predicted a female's provisioning rate to shared offspring (females fed more when paired with darker individuals) in two separate populations, supporting the differential allocation, but not the reproductive compensation hypothesis. Because genetic traits have also been shown to affect parental investment, we evaluated this variable as well and found that a male's paternity did not have significant effects on either male or female feeding rates. Overall, our results suggest that females do not pair with darker males in order to gain direct benefits in terms of his expected levels of parental care to shared offspring, but do themselves invest greater levels of care when paired to darker males. Further, our results are consistent with previous studies which suggest that ventral feather color, not streamer length, is a target of sexual selection in North American populations of barn swallow because females invested more in their offspring when paired to darker mates.     

Variation in tissue-specific gene expression among natural populations

Background

Variation in gene expression is extensive among tissues, individuals, strains, populations and species. The interactions among these sources of variation are relevant for physiological studies such as disease or toxic stress; for example, it is common for pathologies such as cancer, heart failure and metabolic disease to be associated with changes in tissue-specific gene expression or changes in metabolic gene expression. But how conserved these differences are among outbred individuals and among populations has not been well documented. To address this we examined the expression of a selected suite of 192 metabolic genes in brain, heart and liver in three populations of the teleost fish Fundulus heteroclitus using a highly replicated experimental design.

Results

Half of the genes (48%) were differentially expressed among individuals within a population-tissue group and 76% were differentially expressed among tissues. Differences among tissues reflected well established tissue-specific metabolic requirements, suggesting that these measures of gene expression accurately reflect changes in proteins and their phenotypic effects. Remarkably, only a small subset (31%) of tissue-specific differences was consistent in all three populations.

Conclusions

These data indicate that many tissue-specific differences in gene expression are unique to one population and thus are unlikely to contribute to fundamental differences between tissue types. We suggest that those subsets of treatment-specific gene expression patterns that are conserved between taxa are most likely to be functionally related to the physiological state in question.     

Self-fertilization in the white-lipped land snail Triodopsis Albolabris

The breeding system of the polygyrid land snail Triodopsis albolabris was studied in laboratory colonies through the use of allozyme-genetic markers. Isolated virgin individuals self-fertilized only after several months of apparent self-sterility. Isolated pairs appeared to reproduce solely by outcrossing. Overall, the normalized reproductive success of paired individuals was about 86 times greater than that of isolates.
Nine natural populations of this snail were surveyed at eight allozyme loci. All populations were highly polymorphic, and heterozygosity was high and agreed with Hardy-Weinberg expectations. This indicates that selfing is not common in established populations. We conclude that T. albolabris avoid inbreeding by selfing if at all possible. However, if the probability of finding a mate is low (assessed by several months without finding one), lone individuals self-fertilize.     

High Affinity Humanized Antibodies without Making Hybridomas; Immunization Paired with Mammalian Cell Display and In Vitro Somatic Hypermutation

A method has been developed for the rapid generation of high-affinity humanized antibodies from immunized animals without the need to make conventional hybridomas. Rearranged IgH D(J) regions were amplified from the spleen and lymph tissue of mice immunized with the human complement protein C5, fused with a limited repertoire of human germline heavy chain V-genes to form intact humanized heavy chains, and paired with a human light chain library. Completed heavy and light chains were assembled for mammalian cell surface display and transfected into HEK 293 cells co-expressing activation-induced cytidine deaminase (AID). Numerous clones were isolated by fluorescence-activated cell sorting, and affinity maturation, initiated by AID, resulted in the rapid evolution of high affinity, functional antibodies. This approach enables the efficient sampling of an immune repertoire and the direct selection and maturation of high-affinity, humanized IgGs.     

Molecular variation and population structure in endangered <Emphasis Type="BoldItalic">Limonium</Emphasis><Emphasis Type="BoldItalic">bicolor</Emphasis>: genetic diversity of microsatellite markers and amplified fragment length polymorphism analysis

Knowledge and analysis of the genetic structure of an endangered species is important for its conservation and evolutionary process. Simple sequence repeats (SSRs) and amplified fragment length polymorphisms (AFLPs) were used in evaluation of the genetic diversity and population differentiation in Limonium bicolor (Plumbaginaceae), an endangered herb with high medicinal and horticulture value. A total of 117 alleles were detected with an average 5.85 alleles per locus using SSR and 222 bands from AFLP were amplified in six populations. It was found that L. bicolor was characterized by high levels of genetic polymorphism (100 and 83.78%), low levels of total genetic diversity (\(H_{\mathrm{t}}=\) 0.2824 and 0.2424), and moderate degrees of genetic differentiation among populations (\(\Phi _{\mathrm{ST}} =\) 0.284 and 0.251). Analysis of molecular variance (AMOVA) revealed that the main variation component existed within populations (71.56%; 74.93%) rather than among populations (28.44%; 25.07%). Four main clusters were displayed in the UPGMA using TFPGA, which was consistent with the result of principal coordinate analysis (PCA) using NTSYS. Mutations or infrequent gene flow among populations can increase the plant slowly, thus in situ conservation policies should be implemented first for effective and sustainable development. At the same time, ex situ measures, such as those individuals with rare alleles, to maintain the relationships between individuals and populations are also proposed.     

Allozyme Variation in the Rare Gulf Coast Endemic Polygonella macrophylla Small (Polygonaceae)

Abstract Polygonella macrophylla Small is a rare, perennial, primarily gynodioecious plant species endemic to a narrow zone of coastal sand pine scrub habitat along the Gulf of Mexico from Carrabelle, Florida, to Gulf Shores, Alabama (U.S.A.). The species is comprised of a crimson-red flowered form ("rubra"), known from only two populations at the eastern distributional limit of the species, and a white/pink flowered form ("alba") represented by several populations throughout the remainder of the range of the species. An electrophoretic investigation revealed that commonly used measures of gene diversity are very close to expected values in "rubra" given the combination of ecological attributes displayed by the species; however, gene diversity in "alba" is much lower than expected. Population differentiation is high, with estimates of the coefficient of gene differentiation ( G _ST ) indicating that more than 30% of the diversity is among populations. Lack of gene flow among populations, estimated to be at most 0.6 migrating individuals per generation for the species, is a likely cause of greater population differentiation. High inbreeding, detected both within populations and within the species, is suggestive of high rates of self-fertilization in hermaphroditic plants and/or biparental inbreeding in small populations.     

Damage and partitioned mortality of teleosts discarded from two Australian penaeid fishing gears

Six field experiments were perfromed to (1) quantify the scale loss and partitioned (immediate and short-term) mortality of key teleosts discarded from a penaeid seiner and trawler operating in 2 estuaries in southeastern Australia, and (2) assess the utility of modified operational and/or onboard handling procedures for maximising survival. For both gears, several non-target species were caught, handled and discarded according to 2 general categories of treatment ('mild' and 'extreme') representing the plausible limits of severity of commercial operations. The mild treatments involved the shortest conventional deployments of the gears followed by the immediate sorting of catches in water-filled trays, while the extreme treatments comprised the longest conventional deployments and sorting in dry trays. Discards were examined for immediate mortalities and scale loss before sorting onboard, while live individuals of key species, along with appropriate numbers of controls, were released into sea cages and monitored for mortalities up to 5 d. For both gears, there was a trend of higher percentages of immediate mortalities in the extreme treatments, and more scale loss from dead than live seined and trawled silver biddy Gerres subfasciatus, seined tarwhine Rhabdosargus sarba and trawled yellowfin bream Acanthopagrus australis. Despite considerable interspecific variabilities, few intraspecific differences were detected between treatments for the short-term mortalities of live discards; however, for all species, these deaths were greater than those incurred by the controls (most of which survived). The partitioned mortality estimates were combined to provide a range of total mortalities for seined (95.97 and 99.07%, respectively) and trawled (71.74 and 97.64%) G. subfasciatus, seined R. sarba (23.95 and 100%) and trawled southern herring Herklotsichthys castelnaui (100%) and A. australis (3.40 and 35.01%). Because most deaths occurred irrespective of onboard handling procedures, we conclude that simply reducing the duration of gear deployments would provide a first step toward mitigating discard mortality in these fisheries.     

Cloning and genetic variability of a HindIII repetitive DNA in Acrossocheilus paradoxus (Cyprinidae).

Thirty clones of a highly repetitive HindIII fragment of DNA from seven populations of Acrossocheilus paradoxus (Cyprinidae) were isolated and sequenced. The fragment represents a tandemly repeated sequence, with a monomeric unit of 270 bp, amounting to 0.08-0.10% of the fish genome. Higher units of this monomer appear as a ladder in Southern blots. The HindIII satellite DNA family is conserved in three genera of the Cyprinidae. Variation in nucleotide sequences of this repetitive fragment, which is A+T-rich, is distributed both within individuals and among populations. High overall nucleotide divergence (dij = 0.056 +/- 0.001) was detected among clones of the HindIII satellite DNAs of Acrossocheilus paradoxus. Based on the molecular clock hypothesis, the maximum evolutionary rate was estimated to be 5.3 x 10(-7) substitutions per site per year. Lineage sorting may have contributed to the genetic heterogeneity within individuals and populations. Cladistic analyses indicated a closer phylogeographic relationship between populations of the central and south regions in Taiwan.     

MtDNA haplogroups in the populations of Croatian Adriatic Islands

The number of previous anthropological studies pointed to very complex ethnohistorical processes that shaped the current genetic structure of Croatian island isolates. The scope of this study was limited to the general insight into their founding populations and the overall level of genetic diversity based on the study mtDNA variation. A total of 444 randomly chosen adult individuals from 32 rural communities of the islands of Krk, Brac, Hvar and Korcula were sampled. MtDNA HVS-I region together with RFLP sites diagnostic for main Eurasian and African mtDNA haplogroups were analysed in order to determine the haplogroup structure. The most frequent haplogroups were "H" (27.8-60.2%), "U" (10.2-24.1%), "J" (6.1-9.0%) and "T" (5.1-13.9%), which is similar to the other European and Near Eastern populations. The genetic drift could have been important aspect in history, as there were examples of excess frequencies of certain haplogroups (11.3% of "I" and 7.5% of "W" in Krk, 10.5% of "HV" in Brac, 13.9% of "J" in Hvar and 60.2% of "H" in Korcula). As the settlements on the islands were formed trough several immigratory episodes of genetically distant populations, this analysis (performed at the level of entire islands) showed greater genetic diversity (0.940-0.972) than expected at the level of particular settlements.     

Evidence for selection on coloration in a Panamanian poison frog: a coalescent‐based approach

Aim The strawberry poison frog, Oophaga pumilio, has undergone a remarkable radiation of colour morphs in the Bocas del Toro archipelago in Panama. This species shows extreme variation in colour and pattern between populations that have been geographically isolated for < 10,000 years. While previous research has suggested the involvement of divergent selection, to date no quantitative test has examined this hypothesis. Location Bocas del Toro archipelago, Panama. Methods We use a combination of population genetics, phylogeography and phenotypic analyses to test for divergent selection in coloration in O. pumilio. Tissue samples of 88 individuals from 15 distinct populations were collected. Using these data, we developed a gene tree using the mitochondrial DNA (mtDNA) d‐loop region. Using parameters derived from our mtDNA phylogeny, we predicted the coalescence of a hypothetical nuclear gene underlying coloration. We collected spectral reflectance and body size measurements on 94 individuals from four of the populations and performed a quantitative analysis of phenotypic divergence. Results The mtDNA d‐loop tree revealed considerable polyphyly across populations. Coalescent reconstructions of gene trees within population trees revealed incomplete genotypic sorting among populations. The quantitative analysis of phenotypic divergence revealed complete lineage sorting by colour, but not by body size: populations showed non‐overlapping variation in spectral reflectance measures of body coloration, while variation in body size did not separate populations. Simulations of the coalescent using parameter values derived from our empirical analyses demonstrated that the level of sorting among populations seen in colour cannot reasonably be attributed to drift. Main conclusions These results imply that divergence in colour, but not body size, is occurring at a faster rate than expected under neutral processes. Our study provides the first quantitative support for the claim that strong diversifying selection underlies colour variation in the strawberry poison frog.     

Generation,Purification and Transplantation of Photoreceptors Derived from Human Induced Pluripotent Stem Cells

Background

Inherited and acquired retinal degenerations are frequent causes of visual impairment and photoreceptor cell replacement therapy may restore visual function to these individuals. To provide a source of new retinal neurons for cell based therapies, we developed methods to derive retinal progenitors from human ES cells.

Methodology/Physical Findings

In this report we have used a similar method to direct induced pluripotent stem cells (iPS) from human fibroblasts to a retinal progenitor fate, competent to generate photoreceptors. We also found we could purify the photoreceptors derived from the iPS cells using fluorescence activated cell sorting (FACS) after labeling photoreceptors with a lentivirus driving GFP from the IRBP cis-regulatory sequences. Moreover, we found that when we transplanted the FACS purified iPSC derived photoreceptors, they were able to integrate into a normal mouse retina and express photoreceptor markers.

Conclusions

This report provides evidence that enriched populations of human photoreceptors can be derived from iPS cells.     

Dynamics of demographically open mutualists: immigration, intraspecific competition, and predation impact goby populations

Although it is now recognized that mutualistic species are common and can have stable populations, the forces controlling their persistence are poorly understood. To better understand the mechanisms that impact the stability of obligate mutualists, I conducted several field experiments within a sandy coral reef lagoon in Moorea, French Polynesia that manipulated densities of fish (gobies) that interact mutualistically with shrimp. Obligate, mutualistic partnerships of gobies and shrimp are common on Indo-Pacific coral reefs and have been shown previously to interact as follows: shrimp construct burrows in which both species reside, and gobies warn shrimp of predators through tactile communication. Augmentation of gobies by up to 100% above ambient densities within 9 m² plots produced no change in overall density of gobies or shrimp because gobies competed intraspecifically for a limited number of shrimp burrows and smaller gobies were outcompeted by larger individuals. I used predators to assess the impact of goby removal on the stability of goby and shrimp populations. First, although surveys taken throughout the lagoon revealed no relationship between goby and predator densities, predators correlated negatively with the proportion of adult gobies and positively with the proportion of small gobies paired with large shrimp. Second, experimental augmentation of predators resulted in a dramatic reduction of adult gobies within predator-addition plots, but had no impact on overall densities as immigrants rapidly replaced the missing adult gobies. Furthermore, goby turnover resulted in an increase in the proportion of small gobies paired with large shrimp because body sizes of gobies and shrimp in a burrow were similar prior to predator introduction, and predators apparently had a greater impact on gobies than shrimp. The mechanisms that prevent expansion (intraspecific competition) and collapse (immigration) of goby-shrimp populations likely contribute to local-scale stability of mutualistic populations in other terrestrial and aquatic environments.